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Neurology - USMLE secrets


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in smaller muscles, how many muscle fibers does an alpha motor neuron innervate?
just a few - results in finer control of movement
cerebellum influences motor activity on which side?
ipsilateral - projects to contralateral motor cortex and red nuclei whose fibers cross back over
what does the anterolateral system/spinothalamic tract carry?
pain, temperature, crude touch, and pressure
what information do the dorsal columns carry?
fine touch, vibration, concious proprioception
where does the corticospinal tract deccussate?
as it descends through the inferior aspect of the medulla through the medullary pyramids
where do the dorsal columns cross over?
between their nuclei in the brainstem and the thalamus via the arcuate fibers of the medial lemniscus
where do the axons of the spinothalamic tract cross over?
almost immediately after their first-order synapes in the dorsal horn
what are the neurological deficits that occur in Brown-Sequard syndrome?
ipsilateral motor loss and loss of touch, vibration, propriceptive sense; contralateral pain and temperature loss
where do the motor and sensory deficits manifes in patients with a lesion of the internal capsule?
corticospinal tract, dorsal columns, and spinothalamic tract travel to or from the cerebral cortex through the posterior limb - contralateral hemiplegia and contralateral sensory loss
what is the primary mode of analgesic relief of opiods?
inhibition of the spinothalamic tract
what disorder is characterized by loss of pyramidal cells in the cerebral motor cortex that leads to fibrosis of the lateral corticospinal tracts
what is usually spared in ALS?
sensory tracts and cognitive function
what are signs of UMN lesions?
spastic paralysis, hyperactive deep tendon reflexes, and clonus - UMNs are tonically inhibitory to LMNs
what are signs of LMN lesions?
hporeflexia, fasciculations, flaccid paralysis
familial forms of ALS have been associated with what?
mutations in the zinc/copper superoxide dismutase gene, which plays an important role in scavenging free radicals in metabolically active cells such as neurons
periventricular plaques on MRI and oligoclonal bands in CSF are indicative of what?
what is destroyed in Parkinson's?
dopaminergic neurons in the substantia nigra
what kind of drug is bromocriptine?
dopamine receptor agonist
what is benztropine? why is it useful in PD?
anticholinergic - relative excess of Ach because of dopamine deficiency; anticholinergics can be useful in treating motor symptoms
what compound that may be found in ilicit drugs can cause PD?
MPTP - selectively destroys neurons in the substantia nigra
what is the difference between tremor in PD and tremor in cerebellar dysfunction?
PD - resting tremor
cerebellar dysfunction - tremor associated with volitional movements
what is MG often associated with?
what is the pathophysiology of motor weakness in MG?
antibodies to the post-synaptic nicotinic ACh receptors on skeletal muscle fibers
what type of receptors are nicotinic receptors?
ligand-gated sodium channels
what kind of drug is edrophonium?
short-acting cholinesterase inhibitor - increases concentration of ACh in synaptic cleft
what are the long-acting cholinesterase inhibitors?
pyridostigmine and neostigmine
what are the side effects of cholinesterase inhibitors?
excessive PNS stimulation - diarrhea, miosis, bronchospasm, excessive urination, bradycardia, salivation, lacrimation; also sweating because SNS stimulates sweating via ACh
how do you treat organophosphate poisoning?
treatment aimed at reducing total cholinergic activity - palidoxine regenerates active cholinesterase, and anticholinergic atropine
what is Lambert-Eaton syndrome?
AI disease with antibodies to voltage-gated calcium channels located in terminal bouton of presynaptic neurons result in impaired ACh release
what is Lambert-Eaton syndrome often associated with?
paraneoplastic syndromes, particularly small cell CA of lung
bilateral loss of pain and temperature sensation?
what is syringomyelia?
expanded fluid-filled cavity in spinal cord that affects the spinothalamic tract
what produces atrophy of the muscles of hands and hypoactive reflexes of the upper extremities in syringomyelia?
expansion of the syrinx to compress the ventral horns - produces LMN signs
what should you examine for masses in a patient with trigeminal neuralgia?
posterior fossa
what drug is used to treat trigeminal neuralgia?
carbamazapine - reduces rate of nerve transmission by inhibiting voltage-gated sodium channels of neurons
what are CSF findings in MS?
oligoclonal immunoglobulin bands (absent in serum), elevated IgG, and myelin basic protein
this is a disease that involves demyelination of various white matter areas of the CNS
what cell type is attacked and destroyed during an exacerbation of MS?
this syndrome is due to demyelination of peripheral nerves
this type of stroke primarily results from atherosclerosis and subsequent thrombus/embolism or from hypercoaguability in LA (e.g. atrial fibrillation) or LV (after MI)
ischemic stroke
this type of stroke results predominantly from trauma, ruptured AV malformation, ruptured aneurysm, or vessel rupture due to hypertension
how does atrial fibrillation predispose to stroke?
makes it easier for blood to pool and clot within the atria, and the clots can then embolize to brain
what serves the motor and sensory cortex devoted to the contralateral leg?
anterior cerebral artery
what does the MCA supply?
motor and sensory cortex for contralateral upper extremity, head, neck, and face
what artery supplies Broca's and Wernicke's areas?
MCA (typically on left)
occlusion of what can cause left homonymous hemianopsia?
right posterior cerebral artery - supplies visual cortex in occipital lobe
worst headache of life, N&V, stiff neck, photophobia?
subarachnoid hemorrhage
where do you do an LP?
L3-L4 or L4-L5 (SC terminates at L1-L2)
what are the common causes of subarachnoid hemorrhage?
ruptured berry aneurysm, ruptured AVM, head trauma (most common)
patients with PKD most often have berry aneurysms in what location?
bifurcation of anterior communicating artery
almost one-half of cases of this are idiopathic; the rest develop after meningitis, subarachnoid hemorrhage, or intracranial surgery or develop as a result of a tumor
CSF flows from the lateral ventricles into the third ventricle via what?
foramen of Monroe
CSF flows from the third ventricle to the fourth ventricle via what?
cerebral aqueduct (aqueduct of Sylvius)
how is CSF reabsorbed?
empties into dural venous sinuses via arachnoid granulations
trauma that causes unconsciousness followed by lucid interval followed by confusion, lethargy, disorientation
epidural hematoma - intracranial bleeding that dissects periosteal dura away from skull
this is composed of a periosteal layer adherent to bone and a meningeal layer continuous with the arachnoid layer
dura mater
what artery is most commonly involved in an epidural hematoma?
middle meningeal artery - ruptures between dura and skull
this layer attaches directly to brain parenchyma
does CSF show RBCs in an epidural bleed?
no - blood does not reach subarachnoid space where CSF is located
what structures are typically involved in a subdural hematoma?
bridging veins that interconnect the subarachnoid space and the dural (venous) sinuses - more common in elderly people whose brains have atrophied
what carries the efferent part of the corneal reflex?
facial nerve - causes contraction of the orbicularis oculi
what carries the afferent part of the corneal reflex?
anticonvulsant with gingival hyperplasia, nystagmus, and ataxia as side effects?
anticonvulsant with hepatotoxicity as potential side effect?
valproic acid
anticonvulsants that can cause Stevens-Johnson syndrome?
lamotrigine, ethosuximide
anticonvulsants that can cause respiratory depression?
phenobarbital, diazepam
anticonvulsant that can cause agranulocytosis?
anticonvulsant that can cause tremor?
what is the first line treatment for absence seizures?
what effects do most anticonvulsants have on neuronal discharge?
decrease the frequency of neuronal discharge by increasing the threshold for neuronal discharge - most do so by blocking sodium or calcium channels, but benzos activate chloride channels to hyperpolarize neurons
how are AD and Pick's disease different?
AD: diffuse cerebral atrophy
Pick's: selecive atrophy of frontal and temporal lobes
what class of drug is used to treat AD?
cholinesterase inhibitors - AD is associated with selective destruction of cholinergic neurons
if a patient with AD has depression, what drugs should not be prescribed?
TCAs because they have powerful anticholinergic side effects that may exacerbate the cognitive decline due to AD
what is the mechanism whereby short-term memory is consolidated into long-term memory?
long-term potentiation - occurs in hippocamus
what is the second most common cause of dementia in the elderly?
multi-infarct dementia - focal neurologic defects
what is the most common primary brain tumor?
what is the worst grade of astrocytoma?
glioblastoma multiforme
what type of tumor has a characteristic pseudopaliasding arrangement of tumor cells?
glioblastoma multiforme
why are lomustine and carmustine more suitable for treating brain tumors?
belong to a class of alkylating agents - nitrosureas - can effectively penetrate the BBB
what is a meningioma?
benign tumor that arises from the arachnoid cells of the meninges - external to brain and so usually can be surgically resected

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